Modified polyamide membrane

ABSTRACT

A modified polyamide membrane and method for making and using the same. The present invention includes many embodiments including methods comprising contacting a polyamide membrane with certain modifiers, including but not limited to certain oxazoline and/or thiazoline-based compounds, derivatives and polymers thereof. In one embodiment, the surface of a polyamide membrane is coated with a solution including a polyoxazoline and optionally a polyalkylene oxide material, followed by optional heating. Preferred embodiments may exhibit improved performance, e.g. increased rejection of certain species, (e.g. sodium chloride and/or boric oxides such as boric acid or various borate salts), reduced fouling, improved antimicrobial properties, and/or improved storage stability.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional application No.60/899,451 filed 5 Feb. 2007, the entire content of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention generally relates to polyamide membranes including methodsfor modifying such membranes by application of modifiers, including butnot limited to certain oxazoline and/or thiazoline-based compounds,derivatives and polymers thereof.

(2) Description of the Related Art

Polyamide membranes have been used for decades to performing fluidseparations. A classic example of such a membrane is FilmTecCorporation's FT-30™ membrane which comprises a microporous polysulfonesheet with a thin film polyamide layer. The polyamide layer is obtainedby an interfacial polycondensation reaction between a polyfunctionalamine monomer and a polyfunctional acyl halide monomer as described inU.S. Pat. Nos. 4,277,344 and 5,658,460 to Cadotte et al; U.S. Pat. No.6,878,278 to Mickols; U.S. Pat. No. 6,024,873 to Hirose and U.S. Pat.No. 4,950,404 to Chau. Methods of modifying such polyamide membranes aredescribed in U.S. Pat. No. 5,876,602 to Jons et. al.; U.S. Pat. No.5,755,964 and U.S. Pat. No. 6,280,853 to Mickols; U.S. Pat. No.4,888,116; U.S. Pat. No. 4,765,897; U.S. Pat. No. 4,964,998 to Cadotteet. al.; US 2007/0251883 to Niu; U.S. Pat. No. 5,178,766 to Ikeda etal., and U.S. Pat. No. 6,913,694 and US 2007/0175821 to Koo et al. Theentire content of each of the preceding references is fully incorporatedherein. Still other methods for modifying a polyamide membrane aredescribed in WO 2007/133362 to Mickols et al.

BRIEF SUMMARY OF THE INVENTION

The invention includes a modified polyamide membrane and method formaking and using the same. The present invention includes manyembodiments including methods comprising contacting a polyamide membranewith certain modifiers, including but not limited to certain oxazolineand/or thiazoline-based compounds, derivatives and polymers thereof.Preferred embodiments exhibit improved performance including increasedrejection of certain species, e.g. sodium chloride and/or boric acid,reduced fouling, increased antimicrobial properties and/or improvedstorage stability. Many additional embodiments, objectives, advantagesand features are disclosed.

DETAILED DESCRIPTION OF THE INVENTION

The invention is not particularly limited to a specific type,construction or shape of polyamide membrane or application. That is, thepresent invention is applicable to flat sheet, tubular and hollow fiberpolyamide membranes used in a variety of applications including reverseosmosis (RO), nano filtration (NF), ultra filtration (UF), and microfiltration (MF) fluid separations. However, the invention isparticularly useful for modifying composite polyamide membranes such asthose previously described in the Background section. These types ofcomposite membranes are commonly provided as a flat sheet comprising amicroporous support and a “thin film” polyamide layer. Such compositepolyamide membranes are most commonly used in spiral wound modules forRO and NF separations.

The polyamide membrane of the present disclosure can be prepared byinterfacially polymerizing a polyfunctional amine monomer with apolyfunctional acyl halide, wherein each term is intended to refer bothto the use of a single species or multiple species of amines incombination or acyl halides in combination, on at least one surface of aporous support. As used herein, “polyamide” is a polymer in which amidelinkages (—C(O)NH—) occur along the molecular chain.

The polyfunctional amine monomer and polyfunctional acyl halide can bedelivered to the porous support by way of a coating step from solution,where the polyfunctional amine monomer can be coated from an aqueoussolution and the polyfunctional acyl halide can be coated from anorganic-based solution. Although the coating steps can be“non-sequential” (i.e., follow no specific order), the polyfunctionalamine monomer is preferably coated on the porous support first followedby the polyfunctional acyl halide. Coating can be accomplished byspraying, film coating, rolling, or through the use of a dip tank, amongother coating techniques. Excess solution can be removed from thesupport by air and/or water knife, dryers, or ovens, among others.

The polyfunctional amine monomer may have primary or secondary aminogroups and may be aromatic (e.g., m-phenylenediamine,p-phenylenediamine, 1,3,5-triaminobenzene, 1,3,4-triaminobenzene,3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,4-diaminoanisole, andxylylenediamine) or aliphatic (e.g., ethylenediamine, propylenediamine,and tris(2-diaminoethyl)amine). Examples of preferred polyfunctionalamine monomers include primary amines having two or three amino groups,for example, m-phenylene diamine, and secondary aliphatic amines havingtwo amino groups, for example, piperazine. The polyfunctional aminemonomer can be applied to the porous support as an aqueous solution. Theaqueous solution can contain from about 0.1 to about 20 weight percentand more preferably from about 0.5 to about 6 weight percentpolyfunctional amine monomer. Once coated on the porous support, excessaqueous solution may be optionally removed.

The polyfunctional acyl halide is preferably coated from anorganic-based solution including a non-polar solvent, although thepolyfunctional acyl halide may be delivered from a vapor phase (e.g.,for polyfunctional acyl halides having sufficient vapor pressure). Thepolyfunctional acyl halide is preferably aromatic in nature and containsat least two and preferably three acyl halide groups per molecule.Because of their lower cost and greater availability, chlorides aregenerally preferred over the corresponding bromides or iodides. Onepreferred polyfunctional acyl halide is trimesoyl chloride (TMC). Thepolyfunctional acyl halide can be dissolved in an organic solvent in arange from about 0.01 to 10 weight percent, preferably 0.05 to 3 weightpercent, and delivered as part of a continuous coating operation.Suitable solvents are those which are capable of dissolving thepolyfunctional acyl halide and which are immiscible with water, e.g.hexane, cyclohexane, heptane and halogenated hydrocarbons such as theFREON series. Preferred solvents include those which do not pose athreat to the ozone layer and yet are sufficiently safe in terms oftheir flashpoints and flammability to undergo routine processing withouthaving to undertake extreme precautions. Higher boiling hydrocarbons,i.e., those with boiling points greater than about 90° C. such ashydrocarbons with eight to fourteen carbon atoms and mixtures thereofhave more favorable flashpoints than hydrocarbons containing five toseven carbon atoms, but they are less volatile. A preferred organicsolvent is ISOPAR™ available from Exxon Chemical Company.

Once brought into contact with one another, the polyfunctional acylhalide and the polyfunctional amine monomer react at their surfaceinterface to form a polyamide membrane. In embodiments where thepolyamide membrane is formed on a porous support, the polyamide membraneis often referred to as a polyamide “discriminating layer” or “thin filmlayer”. As used herein, “polyamide membrane” can refer to a polyamidemembrane and/or to a polyamide discriminating layer formed on a poroussupport.

The reaction time of the polyfunctional acyl halide and thepolyfunctional amine monomer can be less than one second but contacttime ranges from one to sixty seconds, after which excess liquid mayoptionally be removed, by way of an air knife, water bath(s), dryer, andthe like. The removal of the excess water and/or organic solvent can beachieved by drying at elevated temperatures, for example, from about 40°C. to about 120° C., although air drying at ambient temperatures may beused.

The porous support can be a microporous support. In various embodiments,the microporous support can be a polymeric material containing poresizes which are of sufficient size to permit the passage of permeatethere through but not large enough so as to interfere with the bridgingover of a thin polyamide membrane formed thereon. For example, the poresize of the support can range from 1 nm to 500 nm. Pore diameters largerthan 500 nm, can, in some instances, permit the polyamide membrane tosag into the pores, thus disrupting the flat sheet configuration desiredin some embodiments. Examples of porous supports include those made of apolysulfone, a polyether sulfone, a polyimide, a polyamide, apolyetherimide, polyacrylonitrile, a poly(methyl methacrylate), apolyethylene, a polypropylene, and various halogenated polymers, such aspolyvinylidene fluoride. The porous support can also be made of othermaterials. In some embodiments, the porous support can have a thicknessin a range of 25 μM to 125 μm.

The subject method generally comprises the step of contacting apolyamide membrane with a “modifier” as will be described below. Themethod may be integrated into the method of making the polyamidemembrane, e.g. during the actual formation of the polyamide membraneitself; however, in preferred embodiments the subject method ispracticed after the formation of the polyamide membrane. For example, inone embodiment the subject method is part of a continuous membranemanufacturing process and is implemented just after formation of thepolyamide composite membrane; whereas in other embodiments the polyamidemembrane may formed and stored prior to treatment via the subjectmethod. The step of “contacting” is intended to broadly describe anymeans of bringing the modifier into contact with the polyamide membrane.Similarly, the term “applying” is intended to broadly describe a widevariety of means of bringing the modifier into contact with at least asurface portion of the polyamide membrane such as by way of spraying,air knifing, rolling, sponging, coating, dipping, brushing or any otherknown means. One preferred application technique is to apply a thincoating of the modifier over at least a portion of the outer surface ofthe polyamide membrane by way of a roll contact coater, sometimesreferred to in the art as a “kiss” coater. The modifier is preferablydelivered from an aqueous-based solution. The solution may comprise atleast 0.001, preferably at least 0.01, and more preferably at least 0.1weight percent of the modifier, and less than about 10 and morepreferably less than about 1 weight percent of the modifier. The coatingsolution may also include other constituents including but not limitedto co-solvents, additional modifiers (e.g. polyethylene glycol,polyvinyl alcohol, polyfunctional epoxy materials), along with residual“carry over” from previous manufacturing steps. The modifier coatingpreferable covers a substantial majority of the polyamide surface.

In an alternative embodiment the modifier may be applied to thepolyamide membrane by adding the modifier to a feed liquid which ispassed by (in contact with) the membrane, e.g. after the membrane hasbeen assembled into a module. This alternative application technique ismore suited to embodiments wherein the modifier is a polymer.

Once the modifier is contacted with at least a surface portion of thepolyamide membrane, the resulting membrane is preferably heated, such asby way of a convection air dryer or oven; however other heating meansmay be used, e.g. IR heaters, lamps, etc. While not particularlylimited, the temperatures of such dryers or ovens are preferablydesigned to optimize manufacturing conditions, e.g. line speed, membranechemistry, etc. In several preferred embodiments, the heating stepinvolves passing the polyamide membrane through an oven or convectionair dryer at air temperatures of from about 60 to 120° C., and morepreferably 85 to 100° C., for a few seconds (preferably about 10-60seconds) up to several minutes (and much longer in some embodiments). Asdescribed below, the optional but preferred step of heating facilitatesreaction of the modifier with the polyamide membrane and/or othermaterials present in some embodiments.

The steps of “applying” the modifier and/or “heating” may be conductedconcurrently, but are preferably conducted sequentially. Moreover, thestep of applying and/or heating may include a multiple cycles, e.g.coating followed by heating followed subsequent coating and heating.Furthermore, the step of heating may be utilized prior to the step ofcoating, particularly to remove residual fluids remaining afterformation of the polyamide layer.

The modifiers of the present invention include oxazoline and/orthiazoline-based compounds, derivatives and polymers thereof. This classcomprises materials that are preferably based upon an oxazoline and/orthiazoline ring, particularly 2-oxazoline and/or 2-thiazoline rings.Such rings may include a variety of substituents groups and may bepolymerized to form macromonomers, copolymers or homopolymers—allcollectively referred herein to as “polymers” unless otherwisespecified.

In one embodiment, the modifier is selected from 2-oxazoline and/or2-thiazoline compounds represented by Formula (I):

Y is selected from oxygen (oxazoline) and sulfur (thiazoline), but ispreferably oxygen. R₁, R₂, R₃ and R₄ are not particularly limited. Byway of example, R₁, R₂, R₃ and R₄ may be the same or different from oneanother and can be selected from such diverse groups as: hydrogen;halogen; aliphatic such as alkyl or alkenyl (including substitutedaliphatic such hydroxylalkyl or hydroxylalkenyl; aryl (includingsubstituted aryl include substituents such as hydroxyl, alkyl, halo orhydroxyl); amino; ester; hydroxyl; and polyalkylene oxide (e.g.polyethylene oxide, polypropylene oxide, etc.) preferably including analcohol, ether, epoxide or polyalcohol such as ethylene glycol. In otherpreferred embodiments R₁, R₂, R₃ and R₄ are independently selected fromhydrogen, aryl groups, and alkyl groups having from 1 to 4 carbon atoms(and more preferably 1 to 2 carbon atoms). In instances where one ormore alkyl and/or aryl groups are included, it is preferred that atleast two of R₁, R₂, R₃ and R₄ are hydrogen.

Z is not particularly limited but is preferably a “ring activating”group which allows the ring (oxazole or thiazole) of Formula I to open;and in preferred embodiments to polymerize. A preferred polymerizationproceeds via cation ring opening and propagation (polymerization), asdescribed below. The term “ring activating” group comprises thosesubstituents that destabilize the cationic ring and enhance ring-openingreactivity, and subsequent propagation. While not wishing to be bound bytheory, it is believed that the propagation step is the more critical incontrolling the rate of polymerization. Thus, in preferred embodiments Zis selected from “propagating groups”, i.e. groups that allow andpreferably enhance propagation. It is further believed that electronwithdrawing groups destabilize the cationic ring and enhance 1)ring-opening reactivity and 2) propagation; whereas electron donatinggroups tend to stabilize the ring and/or reduce the ring-openingreactivity. For purposes of oxazole, groups such as hydrogen, phenyls,alkyls, e.g. methyl, ethyl, etc. have sufficient electron effect topermit ring opening and propagation.

By way of example, a preferred catatonic initiated polymerizationreaction scheme for oxazoline is illustrated below, wherein “MeOT” ismethyl tosylate and “Me” is methyl. For this cationic ring-openingpolymerization, the polymerization is governed by two main factors: thenucleophilicity of the monomer that results from the formation of2-oxazoline salt(s) in Equation 1; and the ring-opening reactivity ofthe propagating oxazolinium species formed in Equations 2 and 3. As awhole, the polymerizability is governed by the reactivity of thepropagating species.

Such polymerization may occur after application of the modifier to thepolyamide membrane or before, as will be described below in reference tothe modifier of Formula II.

Applicable ring activating groups (Z groups) include: hydrogen; halogen;aliphatic such as alkyl (e.g. having 1 to 20 carbon atoms but preferably1 to 4 carbon atoms) or alkenyl; substituted aliphatic suchhydroxylalkyl or hydroxylalkenyl; aryl; substituted aryl includesubstituents such as hydroxyl, alkyl, halo or hydroxyl; amino; hydroxyl;and polyalkylene oxide (e.g. polyethylene oxide, polypropylene oxide)preferably including alcohol, ether, epoxide or poly alcohol such asethylene glycol end groups; and having a molecular weight of less thanabout 2000 Daltons, preferably less than about 1000 Daltons, and morepreferably less than about 600 Daltons. When used, the polyalkyleneoxide group may be linear, branched, comb, brush, star or dendritic. Insome embodiments wherein Z is a polyalkylene oxide group, a PEGilationprocess (described below) can be used to link the polyalkylene oxide tothe modifier (e.g. via the no. 2 carbon of the original ring).

Other applicable Z groups includes those which provide an enhancedantimicrobial effect (i.e. result in the modified membrane havingincrease antimicrobial properties), such as aniline,benzene-1,3-diamine, hydroxyl, quaternary ammonium and polybiocides.

Z may also include an internal linking group (“L”) between theaforementioned groups and the no. 2 carbon of the original ring. Thelinking group is not particularly limited and serves as covalent linkagebetween the aforementioned Z groups and the no. 2 carbon of the originalring, as illustrated in Formula (I-A), wherein Z′ is that same as theaforementioned Z groups.

Examples of applicable linking groups include: alkyl, phenyl, ester,ketone, ether, oxygen, sulfide, urethane, beta hydroxy amine, amide,amine, phosphate, sulfone, and thiol, and metals including iron, lead,antimony and phosphorus.

In order to improve coatability, Z is preferably selected from groupsthat provide or otherwise result in the modifier having a solubilityparameter greater than about 18 J^(1/2) cm^(−3/2), preferably greaterthan or equal to 20 J^(1/2) cm^(−3/2), more preferably greater than orequal to 22 J^(1/2) cm^(−3/2), and in some embodiments greater than orequal to 24 J^(1/2) cm^(−3/2); and less than or equal to about 49J^(1/2) cm^(−3/2). If Z is selected from substituents that result in amodifier having a solubility parameter less than 18, the modifierbecomes increasingly difficult to coat on the polyamidemembrane—particularly from aqueous-based coating solutions. Solubilityparameters are widely used and reported in the literature. Solubilityparameters may be determined experimentally but are often based uponcalculated values or estimates based upon experimentally determinedvalues of similar materials. The use of solubility parameters dates backto the early work of Hildebrand using cohesive energy densities, i.e.the square root of the cohesive energy of a material divided by itsmolar volume. Solubility parameters are commonly calculated using aseries of approximations of basic physical parameters. An updatedapproach is described in D. W. Van Krevelen, “Properties of Polymers,Their correlation with chemical structure: their numerical estimationand predictions from additive group contributions,” 3^(rd) Ed.,Elsevier, New York, (1990).

In preferred embodiments, Z is selected from groups that result in themodifier being soluble (i.e. “solubilizing group”) in aqueous-basedsolutions comprising at least 50 weight percent water, preferably atleast 75 weight percent water, more preferably at least 90 weightpercent water, and still more preferably at least 98 weight percentwater. Such aqueous-based solutions may include other componentsincluding alcohols such as: methanol, ethanol, propanol, isopropanol,hexanol, etc; surfactants, and/or other additives. In most embodiments,preferred solubilizing groups include: hydrogen, aryl group, or alkylgroup having from 1 to 20 but preferably 1-4 carbon atoms andpolyalkylene oxide groups. Those skilled in the art will appreciate thatthe total molecular weight of the modifier, the chemical nature of themodifier's terminal end cap groups, and the presence of any co-monomerunits will impact the solubility of the modifier, and that thesolubility of any given modifier in aqueous-based solutions can bedetermined via routine experimentation.

The selection of Y, Z, R₁, R₂, R₃ and R₄ are independent of each other.In some preferred embodiments, R₁, R₂, R₃ and R₄ are each hydrogen, Y isoxygen and Z is a hydrogen, aryl group, or alkyl group having from 1 to20 but preferably 1-4 carbon atoms, such as 2-ethyl oxazoline. In yetanother preferred set of embodiments, R₁, R₂, R₃ and R₄ are eachhydrogen, Y is oxygen and Z is a polyalkylene oxide group (e.g.polyethylene oxide, polypropylene oxide, etc.). The polyalkylene oxidegroup preferably has less than about 60 and more preferably less than30, and still more preferably less than 20 repeating units of alkyleneoxide and preferably comprises a hydroxyl, epoxide or ethylene glycolend group.

The phrase “the same or different” as used herein is intended to meanthat individual groups, e.g. Z, R₁, R₂, etc. are selected independentlyfrom one another, i.e. within an individual compound, within a repeatingunit, and/or between separate compounds or polymers.

In another embodiment of the invention, the modifier is a polymercomprising a repeating unit represented by Formula (II).

wherein R₁, R₂, R₃, R₄, Y and Z are as defined with reference to FormulaI and n is an integer between 2 and about 50,000, preferably from about50 to about 10,000. Z is preferably selected from groups that provide orotherwise result in the modifier having a solubility parameter greaterthan or equal to about 18 J^(1/2) cm^(−3/2), preferably greater than orequal to 20 J^(1/2) cm^(−3/2), more preferably greater than or equal to22 J^(1/2) cm^(−3/2), and in some embodiments greater than or equal to24 J^(1/2) cm^(−3/2); and less than or equal about 49 J^(1/2) cm^(−3/2).In some embodiments, Z is a solubilizing group as previously described.In some preferred embodiments, R₁, R₂, R₃ and R₄ are each hydrogen, Y isoxygen and Z is a hydrogen, aryl group, an alkyl group having from 1 to20 but preferably 1-4 carbon atom, or a polyalkylene oxide group (e.g.polyethylene oxide, polypropylene oxide) preferably including an end capgroup selected from: alcohol, ether, epoxide or poly alcohol such asethylene glycol end groups.

The terminal portions of the polymer (i.e. failing outside the bracketedportion of Formula II) are not particularly limited and preferablycomprise less than about 50 weight percent of the polymer, morepreferably less than about 10 weight percent, still more preferably lessthan about 5 weight percent, still more preferably less than about 2weight percent, and in some embodiments less than about 1 weight percentof the total weight of the polymer. In some embodiments, the terminalportion of the polymer may be non-reactive, or simply the residualportion of the polymerization, (e.g. alkyl and/or hydroxyl). However, inmany embodiments the terminal portions include groups that arechemically reactive with chemical moieties of the polyamide membrane,e.g. form covalent or hydrogen bonds therewith. Examples of such groupsinclude: alcohol, oxazoline, thiol, tolyl, amine, azide, carboxy, styrl,(meth)acrylate, alkenyl, and groups including vinyl groups, andparticularly epoxide, ethylene glycol, and hydroxyl. By way of example,reference is made to Formula (II-A):

wherein E₁ and E₂ are terminal end cap groups and L₁ and L₂ are linkinggroups. E₁ and E₂ may be the same or different, but E₁ is commonlyselected from: hydrogen, alkyl, p-styrlalkyl, m-styrlalkyl,p-aminobenzyl, m-aminobenzyl, 1-3-diaminobenzyl, acrylalkyl andmethacrylalkyl, vinylalkyl, vinylester, vinylether, and polyalkyleneglycol groups. E₂ is commonly selected from hydroxyl, halo, amino,alkylamino, dialkylamino, trialkylamino, diethanolamino,p-styrlalkylamino, m-styrylalkylamino, methacrylate, acrylate,acrylalkylamino, methacrylalkylamino, vinylalkylamino, vinylesteramino,vinyletheramino, and poly(alkylene oxide) amino groups. In preferredembodiments, at least one of the end caps is selected from a reactivegroup such as epoxy, ethylene glycol and hydroxyl, but preferably epoxy.E₁ can be chosen based on the selection of ring-opening initiators. Inaddition, the functionality of E₂ can be introduced by the living natureof a 2-oxazoline polymerization where the living cationic propagatingspecies of 2-oxazolines is terminated (end-capped) with a nucleophilicagent such as an amine containing group. Also, E₁ and E₂ may containvarious polymerizable vinyl groups.

Linking groups L₁ and L₂ are not particularly limited and serve toprovide a covalent link to the end cap groups. In addition to servingthis function, they may also be selected to modify the solubility,hydrophilicity and/or hydrogen bonding capacity of the polymer. Forexample, one or both of L₁ and L₂ may be a simple covalent bond to theterminal end cap group, or an aliphatic group, alkyl phenyl ester,ether, sulfide, urethane, amide, amine, metal, phosphate, polyalkyleneoxide group, or polyvinyl alcohol group linking to the terminal end capgroup. Preferred linking groups include an ether group and alkyl groupshaving from 1 to 12 carbon atoms.

As the combined molecular weight of the linking and end cap groupsapproaches 10 weight percent of the total polymer, the resulting polymercan be better described as block copolymer wherein the term “block”refers to a segment of reoccurring repeating units. In preferredembodiments, a linking group or block preferably comprise equal to orless than 10 weight percent of the polymer, more preferably equal to orless than 5 weight percent, still more preferably equal to or less than2 weight percent, and in some embodiments equal to or less than 1 weightpercent of the polymer. For example, in embodiments where at least oneof the linking groups comprises polyalkylene oxide, the number ofrepeating alkylene oxide units is preferably less than about 60, morepreferably less than 30, and still more preferably less than 20.

The terms “polyalkylene oxide group” or “polyalkylene oxide material”are intended to describe polymers or groups having at least tworepeating units comprising an ether-alkyl group wherein the alkyl groupforming the backbone of the repeating unit comprises from 2 to 3 carbonatoms which can be substituted. Common substituents groups includingalkyl, hydroxyl, hydroxylalkyl, and alkyl groups linked via an epoxylinking group. Specific examples include ethylene oxide and propyleneoxide repeating units. By way of illustration, preferred embodiments ofpolyalkylene oxide groups and materials can be represented by therepeating unit shown in Formula (III):

wherein X is a carbon atom or a chemical bond (e.g. the repeating unitonly comprises two carbon atoms); and R₄ is not particularly limited butis preferably selected from hydrogen, alkyl group (preferably having 1-4carbon atoms but more preferably 1 carbon atom), hydroxyl group, and ahydroxylalkyl group having from 1 to 4 carbon atoms. Preferred examplesare illustrated in Formulae III-A through III-D.

Additional examples of preferred polyalkylene oxide groups and materialsare those described in U.S. Pat. No. 6,280,853 (incorporated in itsentirety). These materials include the repeating unit of Formula IIIwith a terminal portion selected from non-acrylate electrophilic groupsreactive with the functional groups present on the surface of thepolyamide membrane. Specific examples include groups comprising:succinimidyl esters, succinimidyl amides, succinimidylimides,oxycarbonyldimidazoles, azides, epoxides, aldehydes, tresylates,isocyanates, sulfones (e.g. vinyl sulfone), nitropheyl carbonates,trichlorophenyl carbonates, benzotriazole carbonates, glycidyl ethers,silanes, anyydrides, amines, hydroxyl and thiols.

The polyalkylene oxide end cap or block preferably includes a terminalend group selected from alcohol, ether, epoxide or poly alcohol such asethylene glycol. The polyalkylene oxide end cap or block may be linear,branched, comb, brush, star or dendritic.

In still other embodiments, the terminal portions of the polymer may beselected from groups which provide an enhanced antimicrobial effect(i.e. result in the modified membrane having increase antimicrobialproperties), such as aniline, benzene-1,3-diamine, hydroxyl, quaternaryammonium and polybiocides.

In addition to the repeating units of Formula II (and in someembodiments repeating units of Formula III), the subject polymer mayinclude additional (different type) repeating units (i.e. copolymerizedwith other type monomers). However, when included, such co-monomerscontribute to less than about 10 weight percent, more preferably lessthan about 5 weight percent, still more preferably less than about 2weight percent, and in some embodiments less than about 1 weight percentof the subject modifier polymer. The subject polymer preferablycomprises equal to or more than 50 weight percent, more preferably equalto or more than 90 weight percent, still more preferably equal to ormore than 95 weight percent, still more preferably equal to or more than98 weight percent and in some embodiments equal to or more than 99weight percent of the repeating units represented by Formula (II).

The subject polymer may also include the reaction product(s) of polymersdescribed with reference Formula II with other materials such as thepolyalkylene oxide materials described with reference to Formula III, oras described in U.S. Pat. No. 6,280,853 (incorporated herein in itsentirety), and/or polyfunctional epoxy materials as described in U.S.Pat. No. 6,913,694 (incorporated herein in it entirety). Suchpolyfunctional epoxy materials include the reaction products ofepichlorohydrin and a polyfunctional hydroxy, amino and/or amidecompound such as: ethylene glycol, 1,3, propanediol, glycerol,tris(hydroxymethyl)aminomethane, sorbitol, hydroquinon, bisphenol,polyvinyl alcohol, polyvinyl phenol, polyacrylamide, cellulose and itsderivatives, chitosan, etc.

The reaction products of polymers described with reference to Formula IIwith other materials described above may include the chemicalmodification of the terminal portion of a polymer represented by FormulaII with a linking group and end cap group as previously described (withrespect to the repeating units of Formula III). Alternatively, oradditionally the reaction products may include hydrogen bonding and/orentanglement between polymers having repeating units of Formula II andother polymers such as the aforementioned polyfunctional epoxidematerials and the polyalkylene oxide materials described with referenceto Formula III. Such reaction products may include blends of polymers.For example, the subject invention includes the use of blends ofpolyoxazolines with polyalkylene oxides such as poly(ethylene oxide)diglycidyl ether (PEGDE), and/or polyglycerin-polyglycidylethermaterials such as DENACOL 512 available from Nagase Chemtex Corp. Suchblends may include additional polymers such as poly(vinyl alcohol). Suchblends may be formed prior to coating, or may be formed as a result ofsequential coating on the polyamide membrane.

In addition, in some embodiments, the invention includes contacting thepolyamide membrane with an emulsion or microemulsion including aninternal phase of a reaction product of a block poly(2-oxazoline)macromonomer with one or more of styrene, divinylbenzene,1,3-diisopropenylbenzene, polyethylene glycol methyl ether acrylate,polyethylene glycol methyl ether methacrylate, methacrylate, acrylate,vinylacetate, N-vinylformamide, and N-vinylpyrrolidone. Such embodimentsmay include a surfactant.

The subject modifier polymers can be made by a variety of known methods.The preparation, reaction and applications of oxazolines andpolyoxazolines are well known, as described in “Oxazolines: TheirPreparation, Reactions, and Applications” by John A. Frump, ChemicalReviews, Vol. 71, No. 5, 483-505 (1971). See also, Huber et. al. “Newhyperbranched poly(ether amide)s via nucleophilic ring opening of2-oxazoline-containing monomers” Macromolecular Chemical Physics, Vol.200, 126-133 (1999).

One preferred method includes a cationic ring polymerization of2-oxazolines. By way of example, linear poly(2-ethyl-2-oxazoline) andbranched poly(2-ethyl-2-oxazoline) can be prepared by the cationicring-opening polymerization of 2-ethyl-2-oxazoline, shown in ReactionScheme 2.

In another embodiment, a poly(2-oxazoline) macromonomer can be preparedby the cationic ring opening polymerization of a 2-oxazoline followed byend-capping with p-vinylbenzyl chloride (VBC) or meth(acryloyl chloride)(MAC) as shown in Reaction Scheme 3.

wherein “R” is the same “Z” previously defined.

Yet another poly(2-oxazoline) macromonomer can be prepared by aring-opening polymerization of 2-alkyl-2-oxazoline under argon ornitrogen using a mixture of chloromethylstyrene and sodium iodide as aninitiator, as shown in Reaction Scheme 4.

wherein “R” is the same as “Z” previously described.

Additionally, a two-stage cationic ring-opening polymerization of2-oxazolines can also be used with different Z groups to make blockpoly(2-oxazoline) and poly(2-oxazoline) macromonomers. Blockpoly(2-oxazoline) and poly(2-oxazoline) macromonomers can have astructure represented by Formula (IV):

Z is the same or different and is as previously defined with respect toFormula I. In a preferred embodiment, Z may be independently selectedfrom: H, an alkyl having from 1 to 20 carbon atoms (more preferably from1 to 4 carbon atoms), phenyl, and substituted phenyl groups. E₃ isselected from H, alkyl, p-styrlalkyl, m-styrlalkyl, p-aminobenzyl,m-aminbenzyl, 1-3-diaminobenzyl, acrylalkyl and methacrylalkyl,vinylalkyl, vinylester, vinlyether, and polyalkylene glycol groups. E₄is selected from hydroxyl, halo, amino, alkylamino, dialkylamino,trialkylamino, diethanolamino, p-styrlalkylamino, m-styrylalkylamino,methacrylate, acrylate, acrylalkylamino, methacrylalkylamino,vinylalkylamino, vinylesteramino, vinyletheramino, and poly(alkyleneoxide) amino groups.

In some embodiments, E₃ can be chosen based on the selection ofring-opening initiators. In addition, the functionality of E₄ can beintroduced by the living nature of a 2-oxazoline polymerization wherethe living cationic propagating species of 2-oxazolines is terminated(end-capped) with a nucleophilic agent such as an amine containinggroup. Also, E₃ and E₄ can contain various polymerizable vinyl groups.In some embodiments, Z can denote a hydrophilic polymer block,hydrophobic polymer block, or combinations within the materials ofFormula (IV). Z can also represent part of an oxazoline monomer, whichcan provide for desired surfactant properties for emulsionpolymerization with other co-monomers.

In some embodiments, the method of modifying the polyamide membrane caninclude reacting a poly(2-oxazoline) macromonomer or block macromonomer,as shown and discussed herein, with itself or with one or more ofstyrene, methacrylate, acrylate, polyethylene glycol methyl etheracrylate, polyethylene glycol methyl ether methacrylate, vinylacetate,N-vinylformamide, and N-vinylpyrrolidone to form branch, block, graft,brush, and comb polymers. The method can also include contacting thepolyamide membrane with the branch, block, graft, brush, and combpolymers.

In addition, in some embodiments, the method can include contacting thepolyamide membrane with an emulsion or microemulsion including aninternal phase of a reaction product of a poly(2-oxazoline) macromonomeror block macromonomer with one or more of styrene, divinylbenzene,1,3-diisopropenylbenzene, polyethylene glycol methyl ether acrylate,polyethylene glycol methyl ether methacrylate, methacrylate, acrylate,vinylacetate, N-vinylformamide, and N-vinylpyrrolidone. Such embodimentsmay include a surfactant. The subject polymer preferably comprises equalto or more than 50 weight percent, more preferably equal to or more than90 weight percent, still more preferably equal to or more than 95 weightpercent, still more preferably equal to or more than 98 weight percentand in some embodiments equal to or more than 99 weight percent of therepeating units represented by Formula (II).

In some embodiments the compound represented by Formulae (I) and/or (II)can be modified by a PEGilation process. As used herein, “PEGilated” or“PEGilation” refers to the process of covalently coupling apoly(alkylene oxide), e.g. poly(ethylene oxide) structure to anotherlarger molecule. The term “PEGilation” is partially based upon a classof polyethylene oxide polymers having glycol end caps, i.e. polyethyleneglycol, or “PEG”. However, for purposes of the subject invention, theterm “PEGilation” refers more broadly to the use of poly(alkyleneoxides), independently of whether such polymers including glycol endcaps.

In various embodiments, when the polyamide membrane is modified by anoxazoline-based modifying material selected from 2-oxazolines andderivatives of 2-oxazolines, such oxazoline-based modifying material canbe PEGilated by reacting with a poly(alkylene oxide)-containing compoundto create an oxazoline ended poly(alkylene oxide) macromonomer, as shownin Reaction Schemes 5, 6 and 7.

wherein “R” is the same as “Z” as previously described, and “PEG” refersto a ethylene oxide repeating unit.

As illustrated in Reaction Schemes 5, 6, and 7, the 2-oxazolines andderivatives of 2-oxazolines can be, for example, a derivative of2-phenyl-2-oxazoline, 2-(4,5-dihydrooxazol-2-yl)propan-1-ol, and/or a2-methyl-2-oxazoline and the poly(ethylene oxide) containing compoundcan beMeO—[—CH₂CH₂O—]—X, where X is a halide, tosyl (Ts), ormethanesulfonyl (Ms).

Furthermore, macromonomers such as those shown in Reaction Schemes 5, 6and 7 can be polymerized in cationic ring-opening fashion as shown inReaction Scheme 1 to make poly(2-oxazoline) with pendent poly(ethyleneoxide) side chains.

In some embodiments, a mixture of two or more 2-oxazolines can bePEGilated using monomethoxy-PEG-tosylate as a macroinitiator to formcopolymers of the two or more 2-oxazolines.

The PEGilation process can include reacting the 2-oxazolines andderivatives of 2-oxazolines with a poly(ethylene oxide) containingcompound selected from a group including: monomethoxy-poly(ethyleneoxide)-tosylate and PEG-bis(tosylate) to an oxazoline-based modifyingmaterial selected from: a diblock poly(2-oxazoline)-poly(ethyleneglycol) copolymer and/or a triblock poly(2-oxazoline)-poly(ethyleneglycol) copolymers. The diblock and triblock copolymers can be formed,for example, as illustrated in Reaction Schemes 8 and 9.

wherein “R” is the same as “Z” as previously described.

wherein R is the same as “Z” as previously described.

A preferred genus of the polymers of the subject invention comprise“poly(oxazolines),” wherein the term “poly(oxazolines)” includespolymers derived from oxazoline compounds (include substitutedoxazolines), i.e. polymers having repeating units based upon oxazoline.Preferred polymers have a molecular weight greater than or equal toabout 1000 Daltons, preferably greater than or equal to about 5000Daltons and more preferably greater than or equal to about 50,000Daltons; and less than about 2,000,000 Daltons, preferably less thanabout 1,000,000 Daltons and more preferably less than about 600,000Daltons. A preferred class of modifiers comprises poly(2-oxazolines),including poly(2-alkyl-oxazolines) wherein the alkyl group comprisesfrom 1 to 20 carbon atoms, and more preferably 1 to 4 carbon atoms. Anaddition preferred class of polymers include the reaction product(s) ofthe aforementioned poly(oxazolines), (preferably poly(2-oxazolines));and the aforementioned polyfunctional epoxy materials and/orpoly(alkylene oxide) materials preferably having molecular weights lessthan about 2000 Daltons, and more preferably less than about 1000Daltons. A preferred polyalkylene oxide material comprises poly(ethyleneoxide) diglycidyl ether (PEGDE), and/or polyglycerin-polyglycidylethermaterials such as DENACOL 512 available from Nagase Chemtex Corp. Thepoly(oxazolines) and other optional polymers or materials may be reactedand subsequently coated, combined and coated upon the polyamide membranefrom a common aqueous solution, or sequentially coated. Additionalsolvents, reactants, and/or other polymers (e.g. approx. 1 wt %poly(vinyl alcohol) may also be included in the coating solution(s). Thecoating solution preferably comprises at least 0.001, preferably atleast 0.01, and more preferably at least 0.1 weight percent of thesubject modifier, and less than about 10 and more preferably less thanabout 1 weight percent of the modifier. Once coated, the polyamidemembranes are preferably heated at a temperature of from about 60 toabout 120° C. for more than about 1 second, more preferably more thanabout 10 seconds. The heating step may be performed by passing thecoated membrane through a heated air dryer as part of a continuousoperation.

The polyamide membranes of the subject invention may also includehygroscopic polymers upon at least a portion of its surface. Suchpolymers include polymeric surfactants, polyvinyl alcohol andpolyacrylic acid. In some embodiments, such polymers may be blendedand/or reacted with the subject modifiers, and may be coated orotherwise applied to the polyamide membrane from a common solution, orapplied sequentially.

While not wishing to be bound by theory, it is believed that the subjectmodifiers become bound to the polyamide membrane via the subject method.For example, in embodiments were the modifier includes reactive endgroups, (including a reactive Z group) such as a hydroxyl, epoxide,isocyanates, azides, or tresolates, such groups are believed to formcovalent bonds with unreacted amines and/or carboxylic acids groups ofthe polyamide membrane. The optional step of heating a membrane aftercoated with the subject modifiers is believed to facilitate a reactionwith the polyamide membrane. Such heating is also believed to removeresidual water and lead to hydrogen bonding between the modifier and thepolyamide membrane. In other embodiments, the step of heating the coatedmembrane may lead to chemical reaction between the modifier species ofFormula (I) and/or (II) to with polymers represented by Formula (III) orpolyfunctional epoxy materials, thus forming block copolymers which canbe bound with the polyamide membrane as previously described. As anadditional or alternative binding mechanism, preferred embodiments ofthe modifiers are believed to physically entangle with and/orinterpenetrate the polyamide material of the membrane, e.g. via longchains of poly(alkylene oxide) and/or poly(2-oxazonline) becomingphysically entangled with each other and with the polyamide material ofthe membrane.

EXAMPLES

Several example membranes were prepared and then coated with the subjectmodifiers. The “uncoated” composite polyamide membranes used in theexamples were based upon classic FT-30 type composite membranes, i.e.produced by coating a microporous polysulfone support (including anon-woven fabric backing) with an aqueous solution ofmeta-phenylenediamine (MPD) and trimesoyl chloride (TMC). The presentinvention is not limited to FT-30 type composite membranes, nor is theinvention limited to specific polyamide chemistries. For example,polyamide chemistries are typically optimized for specific applicationssuch as RO desalination, RO brackish water, and NF. While such membranesmay all be based upon FT-30 chemistries (e.g. MPD & TMC interfacialpolymerization), the amounts and ratios of constituents typically variesin order to optimize performance for a particular application. Moreover,additives (as described in U.S. Pat. No. 6,878,278) are often utilizedto further optimize or customize performance of the underlying polyamidemembrane for a specific application. While the specific chemistryinvolved in the formation of the polyamide membrane will impact finalmembrane performance, (e.g. flux, NaCl passage, etc.), the followingexamples are intended to demonstrate relative improvement resulting fromthe subject coating which is largely independent of the underlyingpolyamide formation.

The example composite polyamide membranes were prepared by coating amicroporous polysulfone support with an aqueous solution of MPD(approximate MPD concentration of 5.9 wt %). The resulting support wasthen drained to remove the excess aqueous solution. The support wassubsequently coated with a solution of trimesoyl chloride (TMC) inISOPAR™ L (Exxon Corp.) (approximate TMC concentration of 0.16 wt %) toproduce a “thin film” polyamide layer upon the microporous support.After formation of the polyamide layer, the composite membranes werepassed through a water bath at room temperature followed by a subsequentwater bath containing 3.5 wt % glycerin at approximately 100° C. Themembranes were then passed through a convection air dryer atapproximately 65° C. for approximately 50 seconds followed by coatingvia a contact coater with an aqueous solution ofpoly(2-ethyl-2-oxazoline) (PEOX) (MW 500,000) “AQUAZOL” obtained fromPolymer Chemistry Innovation, Inc. Phoenix, Ariz., or PEOX withpoly(ethylene oxide) diglycidyl ether (PEGDE) (MW 526) obtained fromSigma-Aldrich Company. Coatings were performed at various modifierconcentrations as specified in Table 1. The coated membranes weresubsequently passed through a second convection air dryer atapproximately 65° C. for approximately 50 seconds resulting in a thincoating on the surface of the polyamide layer of the composite membrane.The membranes were tested using a transmembrane pressure of 800 psi(approx. 5,520,000 Pascals) and an aqueous test solution comprisingapproximately 32,000 ppm NaCl and approximately 28.6 ppm boric acidmaintained at a pH of approximately 8. The membranes where then storedin a dry state for approximately ten days and re-tested under the sameconditions. The results of the testing are provided in Table 1.

TABLE 1 Coating Boric Acid *Boron Solution Flux NaCl Passage Passage*Flux *NaCl Passage Passage (wt % modifier) (gfd) (%) (%) (gfd) (%) (%)0.05% PEOX 27.0 ± 0.8 0.31 ± 0.05 5.55 ± 0.16 29.9 ± 0.4 0.28 ± 0.046.13 ± 0.16 0.10% PEOX 25.9 ± 0.1 0.25 ± 0.01 5.30 ± 0.09 28.1 ± 0.50.24 ± 0.01 5.76 ± 0.19 0.15% PEOX 25.6 ± 0.4 0.26 ± 0.08 5.20 ± 0.1328.2 ± 0.1 0.22 ± 0.01 5.55 ± 0.32 0.20% PEOX 25.6 ± 0.5 0.22 ± 0.025.21 ± 0.14 28.2 ± 1.2 0.24 ± 0.02 5.78 ± 0.25 0.1% PEOX/ 20.3 ± 0.50.20 ± 0.10 3.97 ± 0.10 22.7 ± 0.4 0.16 ± 0.01 4.37 ± 0.22 0.05% PEGDE0.1% PEOX/ 17.5 ± 0.2 0.18 ± 0.02 3.61 ± 0.15 19.7 ± 1.2 0.19 ± 0.074.04 ± 0.26 0.1% PEGDE Control 32.8 ± 1.5 0.61 ± 0.07 No data 33.9 ± 1.20.82 ± 0.09 No data (no coating) collected collected *Re-tested afterdry storage for approximately ten days

In addition to reducing the passage of certain species (e.g. NaCl,Boron), preferred embodiments of the invention may also exhibit improvedstorage stability. Composite polyamide membranes are commonly assembledand stored in a dry state. Upon re-wetting, such membranes often havenoticeable changes in flux and solute (e.g. NaCl) passage performance.For example, the NaCl passage of the control membrane changed from 0.61%to 0.82% after about 10 days in dry storage. In sharp contrast, the NaClpassage of the experimental membranes coated with the subject coatingsremained relatively unchanged.

Additional examples were prepared, coated and tested in a similar mannerbut with PEOX coatings having different molecular weights, ranging fromabout 50,000 to 500,000 Daltons. The molecular weight of the PEOX hadlittle impact on NaCl passage and flux of the resulting membranes.

While not limited to a particular type of membrane, the subjectinvention is particularly suited for application to composite polyamidemembranes such as those commonly used in RO and NF applications. Suchmembranes include a microporous support and a thin film polyamide layerwhich can be coated with the subject modifier(s).

While principles of the invention are amenable to various modificationsand alternatives forms, particular species have been described by way ofexamples, drawings and detailed description. It should be understoodthat the intent of this description is not to limit the invention to theparticular embodiments described, but rather to cover all modifications,equivalents, and alternatives falling within the spirit and scope of thedisclosure.

1-29. (canceled)
 30. A reverse osmosis or nano filtration polyamide thinfilm composite membrane comprising a microporous support and a thin filmpolyamide layer formed by interfacially polymerizing a polyfunctionalamine monomer with a polyfunctional acyl halide, wherein the thin filmpolyamide layer comprises a coating comprising a polymer comprising apoly(oxazoline).
 31. The membrane of claim 30 wherein saidpoly(oxazoline) comprises a repeating unit represented by Formula (II):

wherein: n is an integer from 2 to 20,000; R₁, R₂, R₃ and R₄ are eachthe same or different and are independently selected from: hydrogen,halogen, an alkyl group having from 1 to 4 carbon atoms, and an arylgroup; Y is selected from oxygen and sulfur; and Z is selected from agroup resulting in said polymer having solubility parameter greater thanabout 18 J^(1/2) cm^(−3/2).
 32. The membrane of claim 31 wherein R₁, R₂,R₃ and R₄ are each hydrogen; Y is oxygen; and n is an integer from 50 to10,000.
 33. The membrane of claim 31 wherein is Z is a solubilizinggroup.
 34. The membrane of claim 31 wherein Z is an antimicrobial group.35. The membrane of claim 31 wherein Z is selected from: hydrogen, analkyl group having from 1 to 20 carbon atoms, an aryl group and apolyalkylene oxide group.
 36. The membrane of claim 30 wherein thepolymer comprises poly(2-ethyl-2-oxazoline).
 37. A method of modifying areverse osmosis or nano filtration polyamide thin film compositemembrane comprising a microporous support and a thin film polyamidelayer formed by interfacially polymerizing a polyfunctional aminemonomer with a polyfunctional acyl halide, wherein the method comprisesthe step of contacting the thin film polyamide layer with a materialcomprising a poly(oxazoline).
 38. The method of claim 37 comprising thestep of applying a solution comprising the material of claim 1 to atleast a surface portion of the thin film polyamide layer.
 39. The methodof claim 38 comprising the step of heating the thin film compositemembrane after the application of solution.